(1) Field of the Invention
The present invention relates to a technique for controlling an optical switch to be used in optical communications, and more particularly to a control method and an apparatus of an optical switch of three-dimensional structure using reflective-type tilt mirrors.
(2) Related Art
It is a known fact that data traffic has been explosively increased due to the recent rapid expansion of the Internet. Therefore, since the constitution of optical networks is shifted from a ring-type to a mesh-type, it is required to set and release (provisioning) optical paths in a more dynamic manner. To attain it, a large-scaled optical cross-connecting (XC) device is required. However, currently used XC devices do not have sufficient capacities, and are restricted by the limitation of electrical process due to the increased signal bit rate. Thus, there is demanded realization of a large-scaled optical switch. For such a demand, attention has been directed to those optical switches of three-dimensional structure adopting tilt mirrors such as fabricated by applying a micro machining (MEMS: Micro Electric Mechanical System) technique, as constitutions suitable for realizing a large-scale such as from a viewpoint of coupling loss or the like.
For the optical switch of three-dimensional structure using the aforementioned MEMS mirrors, for example, as shown in FIG. 24, there is known an optical switch constituted by combining: first and second collimator arrays 11, 12 connected with end portions of first and second optical fiber arrays disposed with two-dimensionally arranged N threads of optical fibers, respectively; and first and second mirror arrays 21, 22 disposed with two-dimensionally arranged N numbers of MEMS mirrors. As shown in FIG. 25, for example, in such an optical switch of three-dimensional structure, an optical signal emitted from one of the first collimator array 11 is reflected by the corresponding MEMS mirror of the first mirror array 21, and the thus reflected light is further reflected by the corresponding MEMS mirror of the second mirror array 22 to thereby input to the corresponding output side optical fiber through the corresponding collimator of the second collimator array 12.
In the optical switch of three-dimensional structure using tilt mirrors such as MEMS mirrors, as aforementioned, there is a possibility that, due to angle deviations among the mirrors, the optical signals are input to the output side optical fibers in a deviated manner, thereby causing a factor to increase a loss within the optical switch. Such a coupling defect is caused by a slight angle deviation, even when the input and output ports are determined the angles of the tilt mirrors at the input and output sides are known values. As such, it is desired to control, with high precision, the angles of the input side and output side tilt mirrors with respect to paths of optical signals corresponding to the input and output channels.
However, for the aforementioned optical switch of three-dimensional structure, no specific techniques concerning the angle control for tilt mirrors have been conventionally proposed.
The present invention has been performed in view of the points as described above, and has an object to provide an optical switch control method and an apparatus thereof, capable of controlling, at a high speed, angles of a plurality of tilt mirrors of an optical switch of three-dimensional structure, by a simplified circuit structure.
To achieve the above object, the present invention provides an optical switch control method which comprises a plurality of mirror arrays each arranged with a plurality of tilt mirrors each having an angle-controllable reflecting surface, and reflects input optical signals sequentially by the respective mirror arrays, to output the optical signals from particular positions, for controlling an angle of the reflecting surface of each tilt mirror on each of the mirror arrays, wherein the tilt mirrors on one mirror array of the plurality of mirror arrays are divided into a plurality of fixed regions. Further, the tilt mirrors on the other mirror array of the plurality of mirror arrays are divided into a plurality of virtual regions, in accordance with connection states of optical paths, such that the tilt mirrors in each of the virtual regions and the tilt mirrors in each of the fixed regions are related to each other so as to make pairs. Then, an angle control of reflecting surfaces of the tilt mirrors is performed in parallel for every related regions, and the angle control of reflecting surfaces of the tilt mirrors in the related regions is performed in a time-division manner corresponding to the optical paths.
According to such an optical switch control method, the angle control of the tilt mirrors on the plurality of mirror arrays is performed in parallel and independently for every related fixed and virtual regions in accordance with the connection states of optical paths, and the angle control of the tilt mirrors in each of the related regions is performed in a time-division manner. Therefore, it becomes possible to simultaneously realize the miniaturization of circuit scale and the shortening of controlling time.
Further, in the above control method, the power of each optical signal after sequentially reflected by the tilt mirrors of the mirror arrays may be detected, to feedback control the angles of reflecting surfaces of the tilt mirrors so that the detected optical signal power is increased. By performing such a feedback control, it becomes possible to control the angles of tilt mirrors with higher precision, thereby enabling to reduce a loss within the optical switch.
Moreover, the angle control of reflecting surfaces of the tilt mirrors may be performed by-conducting the fine adjustment by the feedback control after conducting the rough adjustment based on a previously set initial value. By applying such a control method, it becomes possible to further shorten the controlling time.
In addition, the angle control to be in parallel performed in each related regions may be performed with the synchronization between the respective regions. According to such a control method, it is possible to instantaneously conduct the exchange of virtual regions even in changing the optical path connection over different regions, to thereby avoid a delay of the angle control.
An optical switch control apparatus according to the present invention is constituted by applying the control method as mentioned above. The specific constitution of the control apparatus shall be described in detail in the following embodiments.